Angiotensin II (AII), the biologically active component of the renin- angiotensin system, has a variety of physiological effects in many tissues. In addition, AII is an important pathogenic factor in some forms of clinical and experimental hypertension. Currently, the cellular and molecular mechanism(s) of action of AII are not well understood. AII interacts with two pharmacologically distinct subtypes of cell-surface receptors, AT1 and AT2. AT1 receptors couple to specific G-proteins and mediate most, if not all, of the well known effects of AII. Recently several cDNA clones encoding the AII receptor subtype, AT1, have been isolated and characterized. An AT1 receptor PCR amplified fragment was utilized by our laboratory as a radiolabeled probe to isolate several distinct rat genomic AT1 receptor clones. Preliminary data suggest that there are at least two AII receptor genes. The long term goal of this project is to define the AII receptor gene family and to examine the molecular mechanisms that regulate the expression of these receptors. The Specific Aims are: 1) Characterize, compare and contrast the two distinct rat genomic AII receptor clones by restriction mapping and sequencing. The genes will be expressed and their activities compared. A comparison of tissue specific expression of these genes will also be carried out; 2) The role of AII in the modulation of AII receptor gene expression will be investigated by quantitating and comparing steady state mRNA levels of AII receptors in vascular smooth muscle cells isolated from normotensive and spontaneously hypertensive rats and in tissues from intact rats of these strains infused with exogenous AII or treated with deoxycorticosterone (DOCA) salt. 3) The cis-regulatory mechanism involved in selectively directing the transcription of the AII receptor promoters will be investigated utilizing DNA-mediated gene transfer. These studies will contribute to our basic understanding of the molecular mechanisms underlying AII gene expression in normal animals and will investigate whether AII gene expression is altered in a genetic hypertensive model.